Apparatus for forming and curing continuous elastomeric strip

ABSTRACT

Continuously molding heat curable thermoplastic material into a strip of definite desired cross-section shape and area with means including a cure die in the form of an elongated tube having an entrance end and an exit end and a cross-section similar in shape to the desired shape and greater in area than the cross-sectional area of the desired strip, said cure die including heating means, an extrusion die spaced from the entrance end of said tube and having a cross-sectional area less than the cross-sectional area of said cure die but greater than or equal to the desired crosssectional area of the strip, a lubricating die including means for dispensing lubricant upon said strip, said lubricating die connecting said forming die with said entrance end of said cure die and having a passageway defined therein with a crosssectional area greater than the cross-sectional area of said cure die.

United States Patent Mixellet al.

[54] APPARATUS FOR FORMING AND CURING CONTINUOUS ELASTOMERIC STRIP [72]Inventors: Ronald G. Mixell, Muncie, lnd.; Daryl D. Cerny, Greenville,Ohio [73] Assignee: Ball Corporation, Muncie, Ind.

[22] Filed: Dec. 24, 1969 [21] Appl. No.: 889,828

Related US. Application Data [62] Division of Ser. No. 596,582, Nov. 23,1966, Pat. No.

[52] U.S.Cl ..425/97,425/377,425/l92, 425/378 [51] Int. Cl. ..B29f 3/04[58] FieldofSearcli ..l8/12P,l2M,l2R,l2SE, 18/12 TT, 12 DM; 25/18;264/347 PUMP AND REGULATOR [151 3,659,987 [451 Mayz, 1972 PrimaryExaminer-Robert D. Baldwin Attorney-Campbell & Harris [5 7] ABSTRACTContinuously molding heat curable thermoplastic material into a strip ofdefinite desired cross-section shape and area with means including acure die in the form of an elongated tube having an entrance end and anexit end and a cross-section similar in shape to the desired shape andgreater in area than the cross-sectional area of the desired strip, saidcure die including heating means, an extrusion die spaced from theentrance end of said tube and having a cross-sectional area less thanthe cross-sectional area of said cure die but greater than or equal tothe desired cross-sectional area of the strip, a lubricating dieincluding means for dispensing lubricant upon said strip, saidlubricating die connecting said forming die with said entrance end ofsaid cure die and having a passageway defined therein with across-sectional area greater than the cross-sectional area of said curedie.

4 Claims, 1 Drawing Figure COMPRESSED AIR FROM r STORAGE SUPPLY TANKAPPARATUS FOR FORMING AND CURING CONTINUOUS ELASTOMERIC STRIP Thisapplication is a divisional application of Ronald G. Mixell and Daryl D.Cemy, application Ser. No. 596,582, filed Nov. 23, 1966, now U.S. Pat.No. 3,517,097, issued June 23, 1970.

This invention relates to an extrusion apparatus for forming continuouselastomeric strip. More particularly, this invention relates to a newand improved method and apparatus for producing continuous cured stripfrom moldable rubber materials.

Uncured natural or synthetic rubber may be readily formed into manyshapes and configurations. In the uncured state, it is much likethermoplastic polymers. Thus, uncured rubber can be extruded in manyuseful and often complex cross sections. However, it is necessary tocure the extruded rubber to produce the properties commonly attributedto elastomers.

Curing is accomplished by subjecting the uncured rubber to elevatedtemperatures for a substantial length of time. Though curing is atime-temperature function, there are, of course, optimum temperaturesand corresponding optimum periods of cure.

in the production of solid strip articles, such as that employed forsealing gaskets in large water or sewer pipes, or strips such asmoldings and mountings for window glass, from moldable elastomericmaterials, it has been customary in the art to uniformly form aplurality of strips of a fixed length, often up to 50 feet, and toindividually cure each length of strip in a heating chamber on a batchprocess principle so as to produce a final length of strip material.This approach to the extrusion and curing of elastomeric materials hasseveral drawbacks. For instance, the uncured material does not havegreat strength. Further, while in the uncured state, the material isinitially subject to further loss of strength at cure temperatures.Thus, the more weight at curing temperatures of many extruded crosssections is enough to cause deformation before sufficient curing isaccomplished to provide strength. Also, minor gaseous inclusions whichexpand when released from the confines of the extrusion die can causeextensive porosity in the low strength uncured extruded material.Extrusion, of course, is accomplished at relatively high pressures and,as the material vents from the extruder to atmospheric pressure, thesegaseous inclusions expand greatly, thereby causing a substantial void inthe material. Though many steps, including vacuum treatment of thematerial before extruding, have been taken to avoid gaseous inclusionsin the extrudate, the problem of porosity continues to exist thoughperhaps to a diminished extent.

The above-mentioned batch process presents yet other disadvantages. Forexample, it is advantageous in both the storing and use of stripmaterial to be able to mount continuous finished strip on rolls and towithdraw only the specific amount which is needed for a particular job.This not only reduces the waste resulting from unusable short endlengths of strip, but also eliminates the problem of splicing orconnecting lengths of material in order to form a required long lengthof material. Such a connection is normally difficult to achieve andpresents an unsightly appearance and inherent weakness at the joint.

Thus, it is an object of the instant invention to provide a new andimproved apparatus for forming cured continuous strip from moldableelastomeric material.

It is an additional object of the instant invention to provide apparatusfor forming continuous cured strips in a variety of shapes and sizes athigh speed.

Another object of the instant invention is to provide a new and improvedapparatus for continuously curing rubber strip to produce a product witha cross-sectional area within very close tolerances.

Yet another object of the instant invention is to provide apparatuswherein the rubber strip is cured under substantial positive pressure inorder to minimize porosity of the cured material.

Yet another object of the instant invention is to provide apparatus forcuring strip material while supporting such strip material in a desiredcross section to avoid deformation before the cure strength issufiicient to maintain the desired cross section.

Other objects and advantages of the instant invention will be apparentfrom the following detailed description and drawmg.

According to the instant invention, cured continuous elastomeric stripmaterial is produced by first extruding the uncured material through anextrusion die and thereafter confining the thus extruded material withina cure die. The cure die is maintained at or somewhat above the curetemperature of the particular elastomer stock used and is of such lengthas to retain the strip for an appropriate cure period.

Since the strip is under substantial pressure in the cure die, and sincethe cure die may be or more feet in length, it

' would normally be impossible to force the strip through the cure diebecause of frictional forces. To overcome this obstacle, a lubricatingdie is positioned upstream of the cure die, preferably between theextrusion die and the cure die. A thin film of lubricant is dispersedonto the extruded strip to permit it to pass smoothly through theelongated cure die.

The lubricating die may be merely an appropriately cross sectionedorifice having numerous ports for ejection of the lubricant. However,this die is preferably of a porous material, such as sintered metal, inorder that the lubricant may be forced through the die and on to thestrip material at substantially all points. Though the lubricant isforced through the lubricant containing die under rather substantialpressure, the requirements and tolerances are such that only a smallamount is actually deposited on a unit length of strip. Thus the actualconsumption of lubricant is not of a substantial magnitude.

Only general criteria need be determined to select a satisfactorylubricant. Most water-soluble lubricants are inert to rubber. Of course,the lubricant must be stable at curing temperature, but this is not adifficult requirement. Suitable lubricants include polyalkylene glycolssuch as polypropylene glycol, polyethylene glycol, etc., which areliquid in the desired temperature range. Those skilled in the art willreadily recognize numerous other suitable lubricants equally useful inthe instant invention.

When cured, elastomeric material is reduced in size from the unstressed,uncured size. Thus, in the instant invention, the extrusion die isoversize by a small extent relative to the desired final cross section.However, the extrusion die is slightly smaller in cross section thaneither the lubricating die or the cure die. Though the lubricating andcure die may be of the same size, it is preferable that the lubricatingdie be somewhat larger in cross-section than the cure die and alsolarger in cross-section than the extrusion die. Though differences incross-sectional diameter are desirable, the actual increments arerelatively small and the cure die is seldom larger than 10 percentgreater in area than the extrusion die.

A desirable though not mandatory feature of the instant invention is theprovision of a final constriction, or snubber, to restrict the extrudateas it leaves the end of a cure die. The purpose of this feature ifprimarily to strip most of the lubricant from the material.

It will be recognized that the strip material is usually oversize as itleaves the end of the cure die because of the elevated temperature and,perhaps, incomplete cure. Though the cure may be incomplete, it isadequate to maintain the strip in the desired shape. Of course the stripremains at an elevated temperature for a period after leaving the curedie and thus curing continues to completion. After curing is completeand the strip cools to room temperature, the strip contracts to thedesired dimension despite having passed only through dies larger thanthat size. Of course the dies are only slightly oversize. For instance,relative to the final size of the strip, the extrusion die is 0 to 5percent oversized, and preferably 1 to 2 percent. On the same basis, thelubricating die is l to 25 percent oversize and preferably 15 to 20percent, while the cure die is to 10 percent oversize, and preferably 3to 6 percent. Though an optional feature, the final constriction may be0 to 25 percent undersize relative to the cure die, and preferably l to20 percent.

Referring now to the drawing, there is shown a portion of an extruderhead 10 having an exit passageway 12 therethrough. A forming die 14having a forming passageway 15 therethrough is pressed against head 10and forming passageway 15 is axially aligned with the exit passageway 12in extruder head 10. A lubricating die 17 having a lubricatingpassageway 18 therethrough, axially aligned with forming passageway 15from forming die 14 and exit passageway 12 through extruder head 10, isheld against the opposite side of forming die 14. Lubricating die 17 hasan annular recess 19 around the periphery of its outside surfaceadjacent to forming die 14.

An annular recess 19 is provided in lubricating die 17 at the endsurface adjacent to forming die 14 and extending from the inside surfaceof lubricating passageway 18 to a point approximately midway through thewall of lubricating die 17. Lubricating die 17 has a second annularrecess 20 adjacent annular recess 19, spaced from the inside surface ofpassageway 18, and connecting with annular recess 19. An annularlubricating ring 22 is inserted into annular recess 19 of lubricatingdie 17. Ring 22 may be made of any porous material such as sinterediron. An inlet passageway 23 through lubricating die 17 connects secondannular recess 20 with oil line 24 through connection 25.

The above assembly of extruder head 10, forming die 14, ring 22 andlubricating die 17 is held together by bolts 26 passing through holes ina retaining ring 27, passing through forming die 14, and threadedlymounted in extruder head 10. Retaining ring 27 is a split ring and has aradially inwardly depending lip 29 which is inserted into annular groove30 around the periphery of lubricating die 17. Thus, force from bolts 26presses lubricating ring 22 against lubricating die 17, holding it inplace, and forces lubricating die 17, forming die 14, and extruder head10 together in a sealing connection.

A curing die 32, having a curing passageway 33 therethrough andcomprising two portions 34 and 35, each portion having threads aroundthe outside periphery thereof adjacent each end, abuts the exit end oflubricating die 17 so that curing passageway 33 is axially aligned withlubricating passageway 18. Each portion 34 and 35 of curing die 32 isintermediately supported concentrically within a hollow heat transferhousing 36 by means of a supporting ring 37 extending from the outsidesurface of curing passageway 33 to the inside surface of heat transferhousing 36. Supporting ring 37 has a flange portion 39 which is fastenedto the outside surface of curing die 32 by means of a set screw passingthrough flange portion 39 and bearing against outside surface of curingdie 32. Holes 40 are provided in supporting ring 37 to allow the passageof fluid therethrough.

The end of curing die 32 adjacent to lubricating die 17 is attachedthereto and axially aligned therewith by a sealing connection.Accordingly, lubricating die 17 has an annular, radially outwardlydepending flange 41, the outside peripheral surface of which isthreaded. Flange 41 has an annular groove 42 in its endmost surface intowhich is slidably inserted the end of housing 36. The cavity defined bythe inside surface of housing 36 and the outside surface of curing die32 is sealed at the end adjacent to lubricating die 17 by means of asealing ring 44 threadedly mounted on the entrance end of curing die 32.Sealing ring 44 is fastened to the end of lubricating die 17 by means ofbolts 45 passing through flange 41 and threadedly connecting into holesin sealing ring 44. A lock nut 46 is secured adjacent and engagedagainst the side of sealing ring 44 opposite lubricating die 17. Annularseals 47 and 48 of a compressive material serve to prevent fluid leakagethrough the respective connections. A larger annular seal 49 is mountedaround the outside periphery of housing 36 adjacent to its entrance end.A seal retaining ring 50 is threadedly mounted on the outside peripheryof flange 41 of lubricating die 17 and serves to press seal 49 againstthe connection of housing 36 and flange 41, thus preventing leakage offluid through this connection.

The two portions 35 and 34 of curing die 32 are aligned and connected bya sealing connection. Thus, a sealing ring 52 is threadedly mounted onone end of curing die portion 34 and locked in place by a lock nut. Asecond-sealing ring 53 is mounted on one end of curing die portion 35and locked in place by a lock nut. Sealing ring 53 has portionsextending radially outward into contact with the inside surface ofhousing 36. Sealing ring 52 has an annular groove 54 about its outsideperiphery. A split ring 55 abutting sealing ring 53 and encirclingsealing ring 52 has a lip which extends into annular groove 54 whensplit ring 55 is peripherally tightened around sealing ring 52. Bolts 57pass through split ring 52 and threadedly engage sealing ring 53, thusforcing sealing ring 53 into contact with sealing ring 52 and split ring55, and the end of cure die portion 34 into contact with the end of curedie portion 35. Annular seals 58, 59 and 60 serve to prevent the passageof fluid through joints, respectively.

A connecting ring 62 having flanges 63 and 64 is. mounted around theoutside surface of housing 36 so that'flanges 63 and 64 overlap endportions of housing portions 36, flanges 63 and 64 having threads aboutthe outside peripheral surfaces thereof. Sealing gaskets 66 and 67 areinserted into recessed grooves in the end of flanges 63 and 64. Annularretaining rings are mounted around each flange 63 and 64, and arethreadedly engaged thereon, serving to compress sealing gaskets 66 and67 and provide a fluid-tight connection between housing portions 36.

The cavity defined by housing 36 and curing passageway 33 is blocked atthe exit end remote from lubricating die 17 by a sealing ring 72extending radially from the threaded portion 73 outwardly to contact theinside surface of housing portion 36. Sealing ring 72 is threadedlymounted on threaded portion 73 and held in place by a lock nut. Asnubber die 75 having a passageway 76 therethrough with across-sectional area much less than the crosssectional area of diepassageway 33 abuts the end of cure die portion 35.

Snubber die 75 is mounted within a supporting ring 77 which is attachedto the end surface of sealing ring 72 by means of bolts 78 passingthrough supporting ring 77 and threadedly engaging sealing ring 72.Supporting ring 77 has an annular recess in its side adjacent sealingring 72 and into which the end of housing 36 is slidably inserted. Theoutside periphery of supporting ring 77 is threadedly engaged with theinside surface of a retaining ring 80 which presses a sealing gasket 81into the connection between housing 36 and supporting ring 77.

Snubber die 75 is retained within supporting ring 77 and against the endof curing die portion 35 by means of a retaining ring 82 which isfastened to supporting ring 77 by means of bolts 83 passing throughretaining ring 82 threadedly inserted into supporting ring 77. A lip onretaining ring 82 engages the endmost edge of snubber die 75 and holdsit in position. A passageway 85 is provided at the base of snubber die75 to allow lubricating oil wiped by snubber die 75 from the outsidesurface of a formed and cured strip to be removed.

To provide lubrication to a strip within curing die 32, compressed airis fed through tube 87 into a supply tank 88 into which oil passesthrough tube 89 from storage tank, not shown. Oil is forced from supplytank 88 through tube 90 into a filtering unit 92 and then passes throughtube 93 into a pump 94. The oil is forced by pump 94 under pressurethrough tube 24 into connector 25 and to lubricating ring 22 throughpassageway 23.

Housing 36 has a connection 95 at the exit end thereof and a tube 91through which heat-transfer fluid is returned to a storage tank, notshown. A heater 96 heats fluid from the storage tank which then passesthrough tube 97 into a pump 98, from where it passes through tube 99under pressure through the cavity created between cure die 32 andhousing 36. Thus, a fluid such as hot oil is circulated aroundpassageway through the exit connector 95 and through tube 91 back to thestorage tank.

From the drawing and above discussion it will be apparent that theinstant invention pennits forming and curing of elastomeric materialunder substantial pressure. Thus,the material is positively confined andsupported in the desired shape until curing is essentially complete.Also, the instant invention permits production of cured strip materialsin continuous lengths.

It will be apparent from the above description that variousmodifications in the apparatus described may be made without varyingfrom the scope of the invention. Therefore, the invention is notintended to be limited to the specific details herein described exceptas may be required by the following claims.

We claim I. Apparatus for continuously molding heat curablethermoplastic material into a strip of definite desired cross-sectionalshape and area and for continuously vulcanizing same, comprising anextrusion die having a forming passageway defined therein which is topercent larger in cross-sectional area than the desired strip, feedingmeans connected to one end of said extrusion die and arranged tocontinuously force said material through said forming passageway, alubricating die having a passageway defined therein which is 15 to 20percent larger in cross-sectional area than the desired strip andaxially connected to said extrusion die at the opposite side of saidextrusion die as is said feeding means, lubricating means perimetricallydisposed within said lubricating die and arranged to apply a thin filmof lubricant to the surface of said strip, a cure die having anelongated curing passageway defined therein which is 3 to 6 percentlarger in cross-sectional area than the desired strip, said curingpassageway being axially aligned with said lubricating passageway, andheat transfer means arranged to apply suffrcient heat to said strip tosubstantially cure same while it is moving through said curingpassageway.

2. Apparatus as set forth in claim 1 wherein said lubricating dieincludes a porous ring and means for providing lubricant under pressurethrough said ring to said passageway.

3. Apparatus as set forth in claim 1 wherein a stripper die having apassageway therethrough of a smaller cross-sectional area than said curedie is positioned at the exit end of said cure die.

4. Apparatus as set forth in claim 1 for shaping and curing curablethermoplastic material into continuous strips wherein said extrusion dieis about 1 to 2 percent larger in cross-sectional area than the desiredfinal size of the strip.

1. Apparatus for continuously molding heat curable thermoplasticmaterial into a strip of definite desired cross-sectional shape and areaand for continuously vulcanizing same, comprising an extrusion diehaving a forming passageway defined therein which is 0 to 5 percentlarger in cross-sectional area than the desired strip, feeding meansconnected to one end of said extrusion die and arranged to continuouslyforce said material through said forming passageway, a lubricating diehaving a passageway defined therein which is 15 to 20 percent larger incross-sectional area than the desired strip and axially connected tosaid extrusion die at thE opposite side of said extrusion die as is saidfeeding means, lubricating means perimetrically disposed within saidlubricating die and arranged to apply a thin film of lubricant to thesurface of said strip, a cure die having an elongated curing passagewaydefined therein which is 3 to 6 percent larger in cross-sectional areathan the desired strip, said curing passageway being axially alignedwith said lubricating passageway, and heat transfer means arranged toapply sufficient heat to said strip to substantially cure same while itis moving through said curing passageway.
 2. Apparatus as set forth inclaim 1 wherein said lubricating die includes a porous ring and meansfor providing lubricant under pressure through said ring to saidpassageway.
 3. Apparatus as set forth in claim 1 wherein a stripper diehaving a passageway therethrough of a smaller cross-sectional area thansaid cure die is positioned at the exit end of said cure die. 4.Apparatus as set forth in claim 1 for shaping and curing curablethermoplastic material into continuous strips wherein said extrusion dieis about 1 to 2 percent larger in cross-sectional area than the desiredfinal size of the strip.